The Geant4 geometry modeler

The geometry modeler in Geant4 (a software toolkit for the simulation of the interactions of particles with matter) is a key component of the Geant4 software. It offers the ability to describe the geometrical structure of a detector in a natural way, and has been designed for allowing efficient propagation of particles in the geometrical detector model and exploit at the best the features provided by the Geant4 simulation toolkit. Advanced techniques for optimizing tracking in the geometrical model have been seriously taken into consideration in the design, both in order to optimize the run-time performance and reduce the physical memory consumption when dealing with complex geometrical setups. A great variety of geometrical shapes are defined, including the possibility of combining them with Boolean operations to achieve nearly any possible detector geometry configuration. The major concepts of the Geant4 geometry modeler are here reviewed, with emphasis on recent features introduced in the last releases of the software.